SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1251 PM EDT MON SEP 15 2008
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
 
MODEL COMPARISON (VALID FROM 00Z SEP 15). THE GLOBAL MODELS ARE
IN EXCELLENT AGREEMENT ON THEIR FORECAST OF A MID/UPPER LEVEL
TROUGH TO SLOWLY MOVE ACROSS CENTRAL CHILE/ARGENTINA STARTING ON
DAY 03 AND PERSISTING ONTO DAY 05. THIS FORECAST HAS THE STRONG
SUPPORT OF THE GLOBAL ENSEMBLES...SO CONFIDENCE IS HIGH.

MODELS AGREE ON MID LEVEL TROUGH TO MOVE ACROSS THE EASTERN
PACIFIC ALONG 90W/100W AND SOUTH OF 25S BY 24 HRS. THROUGH 48 HRS
THE TROUGH WILL CONTINUE ALONG 80W/85W...MEANWHILE FOCUSING ITS
SHORT WAVE ENERGY ACROSS CHILE TO THE SOUTH OF CONCEPCION.
BUT...AS THE TROUGH ENTERS THE SOUTHERN CONE...IT WILL FIND A
BLOCKING RIDGE OVER THE WESTERN ATLANTIC/ARGENTINA. AT 48-72
HRS...UNDER INFLUENCE OF THE BLOCKING RIDGE SOME OF THE SHORT
WAVE ENERGY WILL SHEAR SOUTHEASTWARD ACROSS THE DRAKE PASSAGE/
PATAGONIA TO THE SOUTH ATLANTIC. MEANWHILE...ON THE NORTHERN
STREAM...A SHORT WAVE TROUGH WILL SEGREGATE OFF THE COAST OF
CHILE ALONG 76W/78W. BY 72-96 HRS THE TROUGH BEGINS TO MOVE
ACROSS 70W...FOCUSING ITS SHORT WAVE ENERGY ON CONTINENTAL AREA
BETWEEN 25S-35S...WHERE IT WILL SUSTAIN HEIGHT FALLS OF 40-80GPM.
BY 120 HRS THE SHORT WAVE TROUGH WILL ENVELOP AREA BETWEEN 74W-
50W AND SOUTH OF 20S...WHILE CENTERING ON A CLOSED LOW NEAR 34S
66W. THIS WILL FAVOR A DIVERGENT PATTERN ALOFT OVER CENTRAL CHILE
BETWEEN 72-96 HRS...WHICH IN-TURN WILL ALLOW FOR CONVECTION TO
BUILD ON THE ANDES AND ACROSS THE COASTAL PLAINS...FAVORING
RAINFALL AMOUNTS OF 10-15MM. SNOWFALL WILL CONCENTRATE ON
ELEVATIONS ABOVE 4.5-5.0 KM. AT LOW LEVELS...A FRONT MOVES INTO
SOUTHERN CHILE EARLY IN THE PERIOD...AND THROUGH 48-72 HRS IT
ADVANCES ACROSS NORTHERN PATAGONIA-LA PAMPA TO SOUTHERN CUYO. BY
96 HRS A LOW/WAVE WILL FORM ALONG THE FRONT OVER NORTHERN
PATAGONIA...WHICH OCCLUDES INLAND BY 120 HRS. THE OCCLUDING LOW
WILL SUSTAIN A PAMPERO JET ACROSS CENTRAL ARGENTINA. THIS WILL
DRIVE THE ASSOCIATED FRONT NORTH ACROSS CENTRAL ARGENTINA/
MENDOZA BY 96 HRS...AND THROUGH 120 HRS IT PUSHES ACROSS THE
BUENOS AIRES PROVINCE/CORDOBA. AS THE FRONT ENTERS SOUTHERN CHILE
IT WILL SUSTAIN MAXIMA OF 10-15MM/DAY BY 36-48 HRS...WITH MOST
INTENSE OVER CENTRAL CHILE BY 72-96 HRS. AS THE LOW OCCLUDES OVER
CENTRAL ARGENTINA IT WILL SUSTAIN MAXIMA OF 20-30MM...WITH
STRATIFORM PRECIPITATION OVER NORTHERN PATAGONIA/LA PAMPA AND
CONVECTIVE PRECIPITATION ACROSS CORDOBA-BUENOS AIRES PROVINCE.
ALTHOUGH STRONG DYNAMICS ARE TO ACCOMPANY THIS SYSTEM AS IT
ENTERS ARGENTINA...AVAILABLE MOISTURE IS LACKING. SO IF SEVERE
CONVECTION WERE TO DEVELOP BETWEEN MENDOZA-CORDOBA...IT WILL BE
ISOLATED...WITH BEST POSSIBILITY FOR ORGANIZED SEVERE CONVECTION
CONCENTRATING OVER ENTRE RIOS ARGENTINA/URUGUAY.

OVER THE ATLANTIC...MEANWHILE...A 500 HPA TROUGH IS TO EXTEND
BETWEEN 55W-20W AND SOUTH OF 20S THROUGH 72-84 HRS. LATER IN THE
PERIOD THE TROUGH WILL DRIFT EAST OF 45W/50W...TO THEN GRADUALLY
MERGE WITH A BROAD TROUGH ON THE SOUTHERN STREAM FLOW. AT LOW
LEVELS AN ELONGATED FRONT EXTENDS ACROSS THE SOUTH ATLANTIC-RIO
DE JANEIRO/SOUTHERN MINAS GERAIS-MATO GROSSO DO SUL TO NORTHERN
BOLIVIA/SOUTHERN JUNGLE OF PERU. THE FRONT REMAINS NEARLY
STATIONARY THROUGH 72-84 HRS...THEN DRIFTS SOUTH INTO PARAGUAY BY
96 HRS...WITH A WAVE/LOW TO FORM ALONG THIS BOUNDARY OVER CENTRAL
PARAGUAY BY 96-108 HRS AS THE AFOREMENTIONED TROUGH OVER
ARGENTINA INTERACTS WITH THIS BOUNDARY. THE LOW DEEPENS AS IT
MOVES TO SOUTHEAST PARAGUAY THROUGH 120 HRS. INITIALLY CONVECTION
WILL FORM ALONG THE TAIL END OF THE FRONT OVER SOUTHERN JUNGLE OF
PERU...WHERE WE EXPECT DAILY MAXIMA OF 10-20MM IN ISOLATED TO
SCATTERED CONVECTION. OTHER CONVECTION IS EXPECTED OVER NORTHERN
SAO PAULO-RIO DE JANEIRO...TO CONCENTRATE ALONG THE COAST...WITH
DAILY MAXIMA OF 15-30MM/DAY THROUGH 36-48 HRS...AND 10-20MM/DAY
THEREAFTER. AS THE WAVE/LOW FORMS ALONG THE SURFACE FRONT BY 96-
108 HRS...EXPECT A SURGE IN ACTIVITY ACROSS CENTRAL-SOUTHEAST
PARAGUAY-CHACO ARGENTINO/CORRIENTES-MESOPOTAMIA VALLEY...WHERE WE
EXPECT MAXIMA OF 25-50MM/DAY BY 96-120 HRS...TO AFFECT SOUTHERN
BRASIL BY 132 HRS.

AT 200 HPA THE SUBTROPICAL PATTERN OVER NORTHERN SOUTH AMERICA
WILL REMAIN ILL DEFINED DURING THE NEXT 05 DAYS...WITH SHORT WAVE
PERTURBATIONS TO DOMINATE FLOW BETWEEN 05S-20S. THIS IS TO
CONTINUE FAVORING DEEP CONVECTION ACROSS AMAZONAS-PARA IN
BRASIL...WITH MAXIMA OF 20-40MM/DAY THROUGH 36-48 HRS...AND 10-
20MM/DAY THEREAFTER.

GUZMAN...SENAMHI (BOLIVIA)
URRA...DMC (CHILE)
DAVISON...HPC (USA)A$